1. Field of Invention
This invention relates generally to a pressure splitter having a system of orifices with a pressure sensing port located between two of the orifices, at least one orifice having its size vary with temperature. As the temperature controlled orifice(s) change(s) in effective size, the pressure in the sensing port changes. This temperature controlled orifice can be used in conjunction with fixed orifices, or may be used in conjunction with pressure controlled orifices. It can be used in gas or liquid mediums. This device is especially effective in the regulation of carburetor fuel flow as a function of ambient air temperature, or as a function of ambient air temperature and atmospheric pressure.
2. Description of Prior Art
A pressure splitter is a hydraulic or pneumatic device which has an inlet opening to a region of high pressure and an outlet opening to a region of lower pressure. At least two orifices are positioned in series between this inlet and outlet, resulting in an intermediate pressure existing in the region between the two orifices. Each orifice performs a throttling operation in which total pressure drops across the orifice. The pressure drop across both orifices essentially equals the total pressure applied to the splitter, and the intermediate pressure therefore lies somewhere between the inlet and outlet pressures depending on the relative sizes of the orifices. The orifices are usually small in area compared to the chambers to which they are connected, therefore establishing a low fluid velocity ahead of the orifice. The pressure drop across the orifice is a result of the force required to accelerate the fluid medium through the orifice. More than two orifices can be used in the splitter, in various series and parallel combinations, but usually just two series orifices are used. The orifices can be fixed in dimension and consequently their area, but they may also be variable in area, either manually or automatically adjusted by a needle valve, for instance.
Carburetors operate using air pressure differences acting to force a fuel into a bore of the carburetor, and hence to an engine. This fuel flow is through one or more fuel metering orifices. Modern carburetors use multiple systems or circuits to provide the proper fuel/air ratio required for all engine operating parameters. These systems provide a balance between economy and power, enabling maximum power to be delivered by the engine upon demand, but maximum economy whenever possible.
Two basic elements determine the fuel flow in any of these various circuits. The first element is the physical size of the fuel metering orifice, and to a lesser extent, connecting passageways which comprise the particular fuel circuit. The metering orifice is usually sized to be considerably smaller than the other parts of the fuel delivery system, and for the purpose of analyzing fuel delivery, it can be assumed that the metering orifice constitutes the entire fuel delivery system. The second element is the pressure difference existing across the fuel delivery system, or essentially, the pressure existing across the metering orifice. For any given set of conditions, the fuel flow through the fuel delivery system varies approximately as the square root of this pressure difference.
The pressure difference acting across the fuel metering orifice in its most basic configuration consists of the pressure existing on the fuel in the fuel chamber of the carburetor, less the pressure existing in the carburetor bore where the outlet of the fuel delivery system is located, less the head pressure of the fuel. The pressure existing on the fuel in the fuel chamber is controlled by an average reference pressure established by a vent. If the vent is entirely external to the carburetor and its air induction passage, the venting is called external, and atmospheric pressure is the average reference pressure used for the carburetor. If the vent communicates with a region of the bore or other area of the air induction passage, for instance the air cleaner, this venting is called internal. In this case, the average reference pressure used for the carburetor will be slightly less than atmospheric, depending on the location of the pressure sensing end of the vent. Both types of venting, internal and external, are well known in the art.
The pressure existing in the carburetor bore and other parts of the air induction system, and hence existing at the outlet of the fuel delivery system, is determined by engine operating conditions, the position of a throttle valve, a variable venturi if so equipped, and the shape and cross sectional area of the carburetor bore. As a gas, or in this case air, is moving at a velocity, the static pressure (the pressure measured by a pressure sensing orifice with its surface parallel to this flow) will be lower in regions where the velocity is greater. Therefore, as engine speed is increased and the carburetor throttle is opened, air velocity in the bore increases, and pressures perpendicular to the wall of the bore decrease. Also, the bore is normally shaped so that there is a region having a decreasing cross sectional area, called a converging section. The portion having the smallest cross sectional area is called the throat, and air speed will be highest in this region. The converging section and throat comprise the venturi; most carburetors have a venturi with fixed dimensions, but some carburetors have a venturi with operably variable dimensions. It is in the throat that a high speed fuel delivery orifice is usually located. The surface of this fuel delivery orifice is usually parallel to the air flow, or in other words perpendicular to a radius of the bore. Locating the fuel delivery orifice in the throat perpendicular to a bore radius gives the maximum fuel flow possible for a given orifice, bore design, and engine operating condition, since this is the region of the bore where the static pressure is lowest.
The fuel head pressure is simply the pressure required to raise the fuel against gravity a height equivalent to the difference between the level of the fuel delivery orifice in the bore and the level of the fuel in the fuel chamber. It is important that this level be controlled for uniform operation of the carburetor.
There are two basic types of carburetors, float bowl carburetors and wet diaphragm carburetors. In a typical float bowl type carburetor, fuel flows from a larger fuel tank into the float bowl of the carburetor, the level of fuel in the float bowl being determined by a float-actuated valve. This system is well known in the prior art and is discussed in my co-pending applications Ser. Nos. 08/664,187 (now U.S. Pat. No. 5,772,928) and 08/846,815. This fuel level, as discussed above, is important in determining overall carburetor performance. In this case, the venting system used, whether internal, external, or a combination of both, determines the pressure existing in the air occupying the space above the fuel internal to the carburetor. This pressure may contain pressure pulses due to fuel inlet valve instability or due to pressure pulses in the carburetor bore, but the average of this pressure is one parameter which determines average carburetor fuel delivery.
In a typical wet diaphragm type carburetor, fuel flows under pressure from the larger fuel tank to the carburetor, and the pressure internal to the carburetor is controlled by a diaphragm-operated valve. This is also discussed in 08/664,187 and08/846,815. In this case, there is no fuel level specifically, as there is no void internal to the carburetor; it is completely filled with fuel. In this type carburetor, the dry side of the diaphragm, or the side of the diaphragm opposite the side in contact with the fuel, is housed in a chamber which is either internally or externally vented. The average pressure of this chamber, while not being the actual pressure existing on the fuel internal to the carburetor, is the average reference pressure which determines the fuel pressure internal to the carburetor. This average reference pressure exists on the dry side of the diaphragm, while the fuel pressure internal to the carburetor exists on the wet side of the diaphragm. The movement of this diaphragm positions the moveable member of an inlet valve, and hence regulates the average fuel pressure in the carburetor and therefore helps determine average carburetor fuel delivery.
Changes in atmospheric conditions, such as temperature, barometric pressure, and elevation, all of which determine the relative air density, have a considerable effect on the fuel delivery requirements of the engine. Changes in relative air density, without a corresponding change in carburetor tuning, cause a change in the fuel/air mixture ratio, resulting in engine loss of power or a waste of fuel. For instance, a snowmobile engine, which has carburetors tuned or jetted for proper operation at -40 degree Fahrenheit, will run overly rich and get the "blubbers" when run at +40 degrees Fahrenheit, unless the carburetor has the main jets changed to lean the mixture. In extreme cases, the mid-range operation of the carburetor must also be modified by moving or replacing a needle which affects the effective size of the fuel delivery orifice at part-throttle positions. Changing main jets and repositioning or changing mid-range needles is time consuming, results in loss of fuel, and requires partial disassembly of the carburetor. Some carburetors have external mixture screws which adjust an opening in a fuel feed port which parallels the main jet. These systems are expensive to manufacture, and each carburetor must have its own adjustment system. Also these systems work by changing the effective size of the fuel delivery orifice, and not by changing the pressure acting to move the fuel through the fuel delivery system.
Prior art has discussed the use of internal vents to regulate the flow of fuel to an engine. U.S. Pat. Nos. 1,799,585 to Ensign (1931), 1,785,681 to Goudard (1926), 1,740,917 to Beck (1926), and 1,851,711 to Linga (1932) use an internal vent orifice in the carburetor bore which has its pressure affected by the throttle position. All of these devices are complex and add considerably to the cost of machining the carburetor. Except for 1,740,917 to Beck, they are not externally adjustable, and consequently are not usable to change fuel flow necessitated by a change in atmospheric conditions, for instance. They only change the shape of the fuel flow versus engine demand curve, and for any fixed set of operating conditions, the fuel flow is determined and not adjustable. U.S. Pat. No. 1,740,917 to Beck uses an internal vent positioned adjacent the throttle, and uses a manually adjustable external vent to provide an external adjustment of the fuel flow. This system is not automatic in its operation.
U.S. Pat. No. 5,021,198 to Bostelman (1990) describes a carburetor altitude compensation system using a pressure splitter to regulate the fuel flow through the carburetors. In this system, a sealed metering chamber and diaphragm is used to position a valve (choke), which changes the intermediate pressure existing between two orifices. One orifice is located in the line from the venturi region of the carburetor bore, providing a vacuum which tends to decrease the flow of fuel. The other orifice is in the line connected to a region of essentially atmospheric pressure, for instance the air cleaner. This line tends to establish the float bowl pressure at atmospheric pressure, at which maximum fuel flow will occur. The movement of the diaphragm causes a change in the relative size of the two orifices, therefore causing a change in the intermediate pressure existing between the two orifices. This intermediate pressure is applied to the carburetor and is the carburetor reference pressure, and fuel flow varies as the reference pressure varies. This system, like the adjustment in 1,740,917 to Beck, establishes a pressure by balancing two series orifices, one or both orifices being variably throttled. Systems operating on a similar principle using valves and thermodynamic throttling are described in U.S. Pat. Nos. 3,968,189 to Bier (1976), 4,660,525 to Mesman (1987), 4,574,755 to Sato et al. (1986), 4,376,738 to Reinmuth (1983), 3,789,812 to Berry et al (1974), and 3,730,157 to Gerhold (1973). All of these systems use a valve of some nature, usually of a needle type or a sliding type, which is usually operably closed to create an effective valve opening small compared to the area of the conduits to which it is attached, and perform a throttling operation to reduce the total pressure after passing the valve. None of these systems, however, employ an atmospheric temperature controlled orifice in conjunction with a fixed or atmospheric pressure controlled orifice to regulate carburetor fuel flow.
Other carburetor fuel regulating inventions are contained in U.S. Pat. Nos. 3,859,397 to Tryon (1973) and 3,880,963 to Bier et al. (1973). These inventions use pressure or temperature sensing devices to change the effective size of the fuel metering orifice, and do not operate on the principle of affecting the carburetor reference pressure. U.S. Pat. Nos. 3,652,065 to Casey et al. (1972 and 3,861,366 to Masaki et al. (1975) use a complex system of amplifiers, sensers, and electronics or pneumatics to affect the flow of fuel through the carburetor. These two systems also do not affect fuel flow by affecting the carburetor reference pressure.
Valves utilizing materials having different thermal coefficient expansion rates to vary the open area of the valve have been developed. U.S. Pat. Nos. 3,833,171, 3,719,322, and 3,696,997 to Gifford (1974, 1973, and 1972 respectively), 4,759,883 to Woody et al. (1988), and 3,456,722 to Cornelius (1969) all describe valves operating on this principle. These valves are used to control the rate of fluid flow by changing the effective size of a flow controlling orifice, but are not used as a pressure splitter. In other words, there is no provision for a second orifice, used in conjunction with the variable orifice, to establish an intermediate pressure somewhere between the inlet pressure to the valve and the outlet pressure from the valve, and no provision for sensing this intermediate pressure. These devices are simply valves, not pressure splitters, and therefore are ineffective in establishing carburetor reference pressure.
In my co-pending application Ser. No. 08/846,815 I describe a carburetor fuel flow regulator which affects the fuel flow by varying the carburetor reference pressure. This regulator, however, uses a moveable member which changes gas flow speed parallel to an orifice, thereby affecting the static pressure existing in the orifice. Flow is isentropic, and total pressure is conserved. This regulator is not a pressure splitter.